The present invention relates to a testing device for a flowmeter. More particularly, it relates to a testing device for a flowmeter which is fixedly arranged in a pipe, particularly for high medium pressure.
Testing devices of the above mentioned general type are known in the art. In a known testing device for testing a flowmeter arranged in a pipe there is provided a cylindrical gauge container which is selectively switchable by a valve to be connected in series with the flowmeter. The gauge container is provided with a start switch and a stop switch at the beginning and in the end of the measuring section, so that when a measuring piston which is displaced in the gauge container by the fluid to be measured passes the respective switch the adding of electrical impulses of the flowmeter starts or stops so as to provide comparison of the added impulses with the gauge volume of the measuring section. One such testing device is disclosed, for example, in the German Auslegeschrift No. 1,249,547, and particularly in FIG. 5. This testing device is, however, not suitable for high medium pressure, since it is unavoidable that the wall of the gauge container elastically expands under the action of the high medium pressure whereby the gauge volume increases and the test results become false. Moreover, the valve arrangement for directing the fluid flowing in the pipe into the gauge container provided in the bypass conduit is composed of several check valves which are arranged in the bypass conduit before and after the gauge container and of a check valve seated in the pipe. Thereby the testing device is structurally very expensive, and a considerable time is required for deflecting the medium flow through the gauge container. Moreover, since the start and stop probes correspond to raising fluid level in the gauge container, the pressure medium must leave the gauge container prior to each testing step. Therefore an additional discharge valve with a discharge line is required and an emptying time which considerably delays the testing step must be taken into consideration. In addition the gas or air located above the fluid level in the gauge container is pressed into the pipe, whereby the conveyed medium is mixed in undesirable manner with the gas or air. Also, the raising fluid level in the gauge container is not quiet because of the flow movement of the fluid and thereby the switching point for the start and stop of the testing process is not accurate.
The German Auslegeschrift No. 1,249,547 discloses in its FIG. 1 a testing device in which the measuring section is provided in a longitudinal measuring pipe with a measuring piston which is displaced by the fluid to be measured from its one end position to its other end position. A start switch is arranged in the beginning of the measuring section in the measuring pipe, and a stop switch is mounted in the end of the measuring section. They are actuated during movement of the measuring piston and start or stop the adding of the throughflow impulses. This testing device is also not suitable for high medium pressure, inasmuch as the wall of the measuring pipe can also elastically expand under the action of high pressure, whereby the gauge volume of the measuring section is abnormally increased. Moreover a leakage between the measuring piston and the pipe wall because of the expansion is counted here, which also results in visible volume increase and thereby a measuring error. The bypass conduit can remain filled by the intermediate switching of the measuring piston which displaces in the measuring pipe. However, here a row of check valves is required, and additionally also several changeover switches are needed to supply the measuring fluid in the bypass conduit from the desired side in the measuring pipe which operates in both directions. Thereby considerable pressure shocks in the conduit can take place when the valves operate not synchronously.